1. Field of the Invention
The present invention generally relates to vehicle suspension systems. More specifically, the present invention relates to an improved shock absorber system to be incorporated into the suspension system of a bicycle.
2. Description of the Related Art
Bicycles intended for off-road use, i.e., mountain bikes, commonly include a suspension assembly operably positioned between the rear wheel of the bicycle and the frame of the bicycle. The suspension assembly typically includes a shock absorber configured to absorb forces imparted to the bicycle by bumps or other irregularities of the surface on which the bicycle is being ridden. However, an undesirable consequence of incorporating a suspension assembly in a bicycle is the tendency for the shock absorber to absorb a portion of the power output of a rider of the bicycle. In some instances, i.e. when the rider is standing, the proportion of power absorbed by the shock absorber may be substantial and may drastically reduce the efficiency of the bicycle.
Vehicle shock absorbers utilize inertia valves to sense rapid accelerations generated from a particular part of the vehicle. Inertia valves are also used to change the rate of damping in the shock absorber depending on the magnitude of the acceleration. As an example, the inertia valve assembly may be arranged to adjust the damping of the rear shock in accordance with accelerations that are generated by the body of the vehicle differently than it would adjust the damping of the rear shock for accelerations that are generated by the rear wheel of the vehicle.
One example of the type of shock absorber that utilizes an inertia valve to distinguish rider-induced forces from terrain-induced forces and is described in U.S. Pat. No. 6,604,751 B2. According to U.S. Pat. No. 6,604,751, the shock absorber of U.S. Pat. No. 6,604,751 is positioned between the swing arm and the main frame to provide resistance to the pivoting motion of the swing arm. The rear shock absorber includes a peripherally located fluid reservoir that is connected to the swing arm at a distance away from the shock body, and is hydraulically connected to the main shock body by a hydraulic hose. In one embodiment, the reservoir of U.S. Pat. No. 6,604,751 is connected to the swing arm portion of the bicycle above the hub axis of the rear wheel.
The inertia valve assembly of U.S. Pat. No. 6,604,751 discloses an inertia valve attempting to overcome the effects of external forces and manufacturing defects that inhibit the motion of the inertia valve with the use of one or more “Bernoulli Steps” on an interior surface of the inertia mass. Also, the peripherally located reservoir of U.S. Pat. No. 6,604,751 discloses a blowoff valve that allows for an increased flow rate after a minimum threshold pressure is exceeded inside the blowoff chamber. Typically, this will occur when the bicycle hits a severe bump. Further, the refill ports and the axial blowoff passages of the shock absorber of U.S. Pat. No. 6,604,751 are located on the top surface of the reservoir.
However, the blowoff valve of U.S. Pat. No. 6,604,751 is not adjustable. That is, no mechanism is provided for adjusting the opening threshold pressure of the blowoff valve. A rear shock absorber sold on the 2007 model year and 2008 model year Epic bicycle sold by the assignee of the present application, Specialized Bicycle Components, Inc., includes a main shock body and a reservoir. An inertia valve mechanism and a compression valve mechanism are provided in the reservoir. The compression valve mechanism includes a one-way valve having one or more shims that normally close one or more ports in a reservoir piston. The compression valve mechanism also includes a needle-and-orifice-type valve, or bleed valve, which includes a needle member that is movable via an external adjustment knob to vary an amount of fluid flow through the orifice. However, due to the location of the compression valve mechanism within the reservoir between the inertia valve and a floating piston, the adjustment rod that couples the needle member with the adjustment knob must pass through either the floating piston or the inertia mass. In the actual Epic shock absorber, the adjustment rod passes through the floating piston, which increases the complexity of manufacturing and assembling the shock absorber. Thus, the need exists for an improved rear inertia valve shock that provides advantageous adjustment features and is relatively easy and cost-effective to manufacture.